Multiple layers of thin veneers are used to form plywood. It is known that plywood can be made from a variety of different veneer species having varying strengths and densities. Typically, the veneer from a stronger species will be used for the individual face and back plies of the plywood, while other veneers, including weaker and/or lower grade veneers, are used for the inner plies. In the past, the individual veneer sheets, upon exit from the veneer dryer, would often be curled or otherwise distorted to some extent. This distortion of the veneer sheets which occurred during the drying process was due to various characteristics of the veneer wood itself. Sometimes the veneer would be curled so badly that it could not be used. To overcome this problem with respect to veneer used for inner plies, the veneer was incised at selected intervals by a plurality of knife-like blades, to "relax" the veneer from its curled state. When relaxed in this manner, the veneer could be readily flattened and used in plywood, and could even be edge glued.
Such incising of veneers, however, is accomplished following the drying step. With some veneer sheets, the curling of the veneer during drying becomes sufficiently extreme to "plug up" the dryer, necessitating a temporary shut-down of the dryer to remove the material and then a restart. This results in a loss of time and material in the veneer manufacturing process and decreases operator efficiency. When it became known that the veneer produced from near the center of a log was likely to result in the degree of curling during drying which would lead to interruption of dryer operation, the veneer peeling process was typically terminated for a particular log at that point, even though additional quality veneer could otherwise be obtained from the log.
As mentioned above, treatment of veneer to defeat curling and other distortions has in the past only been done following the drying step. It is known, however, to use incisor rollers on green veneer which are similar to those used to relax curled veneer, as shown in U.S. Pat. No. 4,655,8669 to Tellman et al, to laterally expand the veneer, thereby in effect increasing the size of the veneer sheet by some amount. This technique typically leads to significant savings in material. The use of incising to expand veneer, however, does lead to weakness in the veneer and resulting breakage, which are undesirable. These problems would tend to point away from the application of the Tellman teaching to green veneer for other purposes such as to minimize curling and distortion, where veneer strength is important.